Congratulations, there's nothing to correct, so I'm just going to suggest you use a bit more precise vocabulary and use connectors to combine clauses into longer sentences:

Hello everyone! This is my self-introduction:

I am learning English now, so (or "because," depending on what you mean) I'd like to make new friends all over the world. I'd like to connect with you via email or wechat. I am a native Mandarin speaker, so if you want to practice (if you're interested in practicing) your Mandarin, I can help you. For your information, I'm not a teacher; I just want to make new friends here, communicate with each other learners (this is not really reflexive, since you're talking about yourself), and talk about different cultures and life styles. During our communication we can help each other a lot, and it will be better and more interesting than taking a class online.